The present invention relates to an apparatus for imparting a braking force to an advancing strand. In the present application, the term "strand" is intended to encompass all linear structures, such as wires, yarns, bands, ropes, and the like.
A strand brake is disclosed in U.S. Pat. No. 3,830,050, which relates to a wire stranding machine. The known brake is universally usable for the adjustment of the tension of a strand, and it is used in particular for the adjustment of the tension of wires, bands, yarns, etc., which are withdrawn from a freely rotatable supply spool with a brake. Such known brakes have the disadvantage that the braking effect and, thus, also the increase of the tension are dependent on the amount of the strand tension. Another disadvantage is that despite the regulation, the tension increases as the spool empties from the full to the empty condition, when the brake is operative on the spool. This increase of tension is larger, the greater the tension is.
Yet another disadvantage is that the brake is adjusted to a certain strand tension right from the beginning. Although this tension may be optimal for the stationary operation, it can nonetheless be too high for the threading of the strand and for the startup of the machine, and can lead to difficulties, in particular to strand breaks. This applies especially to the use of the strand brake in machines in which the strand which is restrained by the brake, passes subsequently through a balloon. In this instance, the strand forces which develop in the balloon will not suffice to overcome the braking forces, when the machine is started up.
It is an object of the present invention to provide a strand brake which operates such that, especially when the strand is withdrawn from a supply spool, the tension of the strand has a controlled, desired gradient, that is low in particular at a standstill and at a startup, and remains substantially constant in the stationary operation, and that possible changes are likewise independent of the amount of the strand tension.